Abstract: The microstructure of intragranular ferrite and the impact of intragranular ferrite on the mechanical property of steel is analyzed to find out that intragranular ferrite can markedly improve the impact toughness of steel. The nucleation mechanisms of intragranular ferrite are expounded particularly to show that the nucleation mechanisms of intragranular ferrite are not perfect enough to develop a uniform nucleation mechanism. The inclusions such as titanic oxides, manganese sulfide and rare earth oxides which can promote the nucleation of intragranular ferrite are introduced to indicate that the compound inclusions with titanium are perfect nucleation core. The impacts of inclusions size and the cooling rate on the nucleation are analyzed. The microstructure control technologies for intragranular ferrite are presented, and the result shows that the addition of titanium and boron and the addition of titanium and magnesium are better than the single addition of titanium.